1. Field of the Invention
The present invention relates generally to semiconductor devices, and in particular, to a semiconductor device in which its elements are covered with a protective insulating film in order to prevent the elements from being changed due to extraneous factors in the environment such as moisture, stress, etc. The present invention further relates to the manufacturing method of such a semiconductor device.
2. Description of the Background Art
In a semiconductor device, after formation of elements on a semiconductor substrate, the elements are covered with a protective insulating film, and then housed into a mold resin package or a ceramic package in order to prevent the effect of extraneous factors in the environment such as moisture, stress, etc.
FIG. 1 is a sectional view of a conventional mold resin sealed semiconductor device. FIG. 2 is an enlarged view of A part in FIG. 1.
Referring to FIG. 1, a chip 21 is provided on a die pad 23a. On the chip 21 formed are elements. An electrode of the chip 21 and a lead 23b are electrically connected by a bonding wire 24. The die pad 23a together with the lead 23b are referred to as a lead frame 23. On the chip 21 formed is a protective insulating film 5. The chip 21 is sealed by mold resin sealing agent 25.
Referring to FIG. 2, further detailed description will be provided on the structure of the above-described chip. In the following, a DRAM (Dynamic Random Access Memory) device will be described as an example. A DRAM element 2 (stacked capacitor cell) is formed on the surface of a silicon semiconductor substrate 1. On the DRAM element 2 deposited is a first insulating layer 3. A first interconnection 4 is formed on the first insulating layer 3. A protective insulating film 5 is deposited to cover the first interconnection 4. The protective insulating film 5 is provided with an opening 5a for exposing a bonding pad 6. The bonding wire 24 is connected to the bonding pad 6 to connect the external lead 23b and the first interconnection 4.
Now, description will be provided on the manufacturing method of the DRAM device shown in FIG. 2 in conjunction with FIGS. 3A-3F.
Although multi-interconnection structures are generally known as interconnection structures which are formed of polysilicon interconnections, high melting point metal silicide interconnections, high melting point metal interconnections, aluminum interconnections, etc., the case shown in FIG. 2 in which the first interconnection 4 is of an aluminum interconnection and of a single layer interconnection structure will be described in the following by way of simplification.
Referring to FIG. 3A, the DRAM element (stacked capacitor cell) 2 is formed by providing an oxide film for element isolation 301, a transfer gate electrode 302, an impurity diffusion layer 303, a word line 304, a storage node 305, a capacitor insulating film 306 and a cell plate 307 on the surface of a silicon semiconductor substrate 1.
Now, referring to FIG. 3B, a first insulating film 3 is deposited onto the surface of the silicon semiconductor substrate 1 on which the DRAM element 2 is formed. Then, a contact hole 308 is formed in a desired part in the first insulating film 3 by a photolithography method and an etching method. An aluminum interconnection to be a first interconnection is formed as a bit line. The first interconnection 4 includes the bonding pad 6.
Referring to FIG. 3C, a silicon oxide film, i.e. the protective insulating film 5 is deposited onto the surface of the silicon semiconductor substrate 1 by using a Chemical Vapor Deposition method (CVD method hereinafter) using, for example, a silane (SiH.sub.4) gas and a nitrous oxide (N.sub.2 O) gas at a film deposition temperature ranging from 300.degree.-450.degree. C. and using heat or plasma .
Referring to FIG. 3D, the opening 5a is formed in the protective insulating film 5 by a photolithography method or an etching method for exposing the bonding pad 6 to perform wire bonding.
Now, referring to FIGS. 1 and 3E, the semiconductor substrate 1 with the elements formed thereon is severed by dicing to be the semiconductor chip 21. The semiconductor chip 21 is then adhesive-bonded to the die pad 23a of the lead frame 23 by soldering or with conductive resin. Then, the bonding pad 6 and the lead 23b of the lead frame are connected by the bonding wire 24.
Referring to FIG. 3F, finally the device is entirely packaged by the mold resin sealing agent 25.
Other than the above-described silicon oxide film, a silicon nitride film formed by a CVD method using silane and nitride or ammonia, a silicon-oxy-nitride film formed by a CVD method using nitrous oxide, and the layered structure of these films, etc. are used as a protective insulating film.
The conventional mold resin sealed semiconductor device structured as described above possesses the following problems.
With development of higher performance semiconductor devices, the area of the semiconductor chip 21 in FIG. 4 tends to be larger. When packaging a semiconductor chip having such a large area, as shown in FIG. 4, compressive stress 26 created by the mold resin 25 gives rise to a problem. In other words, the compressive stress 26 of the mold resin 25 is applied to the surface of the semiconductor chip 21, and, therefore, the first interconnection 4 (aluminum interconnection) is mechanically deformed (sliding phenomenon of the aluminum interconnection) as shown in FIG. 5 (an enlarged view of A part in FIG. 4), thereby producing a crack 8 in the protective insulating film 5. The existence of such a crack in the protective insulating film 5 permits moisture 9 entering through the mold resin 25 from the outside to reach all the way to the first interconnection 4, thereby corroding the first interconnection 4. Such a corroded portion 10 degrades the reliability such as moisture resistance, etc. of the semiconductor device.
One solution to such a problem is to increase the mechanical strength of the step portion of the first interconnection 4 to a level sufficient to tolerate the compressive stress 26 of the mold resin 25. In a silicon oxide film of silane type deposited in a conventional method, e.g. a plasma CVD silicon oxide film of SiH.sub.4 +N.sub.2 O type, a film deposition reaction (in accordance with a method of forming a film in which film components are formed by a reaction in vapor and are deposited on a substrate) takes place mainly in layers, and, therefore, the step coverage at the step portion 31 of the first interconnection 4 is poor. As shown in FIG. 6B, even with a protective insulating film 32 being deposited to be thick (1 .mu.m), the step coverage is not good so that the film thickness of the step portion 33 of the first interconnection 4 cannot be made large enough. This method cannot therefore be employed as a solution for the above described problem.
This applies to other cases in which a silicon nitride film deposited with silane, a silicon-oxy-nitride film, etc. are used.
Recently, use of a plasma CVD.silicon oxide film using tetra methoxy silane (TEOS) and oxygen as a film having a superior step coverage has been reported, but a resultant film is a silicon oxide film which is not as fine as a silicon nitride film or a silicon-oxy-nitride film used conventionally as a protective insulating film. The film is therefore inferior in terms of a barrier characteristic to moisture coming in from the outside, and cannot tolerate compressive stress by mold resin. The silicon oxide film is therefore insufficient in terms of mechanical strength.
One object of the present invention is to improve the step coverage of a protective insulating film in a semiconductor device having a protective insulating film.
Another object of the present invention is to provide an improved semiconductor device having a protective insulating film to tolerate compressive stress by mold resin.
A further object of the present invention is to provide a semiconductor device having a protective insulating film which has improved reliability such as moisture resistance.
Yet another object of the present invention is to provide a manufacturing method of a semiconductor device improved to tolerate compressive stress by mold resin and having an improved reliability level such as moisture resistance.
In order to achieve the above-described objects, a semiconductor device in accordance with the present invention includes a semiconductor substrate on which elements are formed, a patterned interconnection provided on said semiconductor substrate and electrically connected with said elements, and a silicon-oxy-nitride film provided on said semiconductor substrate so as to cover said interconnection pattern. The above described silicon-oxy-nitride film is deposited in a CVD method using plasma, using a mixture gas including an organic silane gas and a nitriding gas.
In accordance with a preferred embodiment of the present invention, the above-described silicon-oxy-nitride film is formed at a film formation temperature in the range of 300.degree.-450.degree. C. under a film formation pressure in the range from 10-100 Torr.
In a semiconductor device in accordance with the present invention, a protective insulating film is formed of a silicon-oxy-nitride film deposited by a CVD method using plasma, using gas including an organic silane gas and a nitriding gas. The silicon-oxy-nitride film has superior step coverage because its film deposition reaction (specific to a film formation process using organic silane) takes place mainly on the surface of the substrate. When depositing the above-described silicon-oxy-nitride film on the interconnection pattern, the film thickness of the protective insulating film is not formed to be thin in the step portion. Consequently, the mechanical strength of the protective insulating film can be increased to a level sufficient to tolerate compressive stress by the mold resin. The mechanical deformation of the interconnection pattern or the formation of cracks in the protective insulating film in accordance with the deformation can thus be prevented.
Also, the insulating film including a silicon-oxy-nitride film including N atoms having a small radius, is finer than a silicon oxide film, thereby providing a high barrier characteristic to moisture coming in from the outside. A semiconductor device having superior reliability such as moisture resistance, etc. is thus provided.
A semiconductor device in accordance with another aspect of the present invention includes a semiconductor substrate on which elements are formed, an interconnection pattern provided on said semiconductor substrate and connected electrically with said elements, and a silicon-oxy-nitride film provided on said semiconductor substrate so as to cover said interconnection pattern and including 0.01-0.5 wt % of hydroxyl group.
The manufacturing method of a semiconductor device in accordance with a further aspect of the present invention includes the steps of forming elements on a semiconductor substrate, forming an interconnection pattern connected electrically with said elements on said semiconductor substrate, and depositing a silicon-oxy-nitride film on the above interconnection pattern. The said silicon-oxy-nitride film is deposited by a CVD method using plasma by using a mixture gas including an organic silane gas and a nitriding gas at a film formation temperature in the range from 300.degree. to 450.degree. C. under a film formation pressure in the range from 10 to 100 Torr.
In accordance with the manufacturing method of the semiconductor device of the present invention, superior step coverage is provided because a film deposition reaction (specific to a film formation reaction using organic silane) takes place mainly on the surface of the substrate. Therefore, when depositing the film on the interconnection pattern, the protective insulating film is not formed to be thin in the step portion. Consequently, the mechanical strength of the protective insulating film can be increased to a level sufficient to tolerate compressive stress by the mold resin. The protective insulating film formed in accordance with the method, being a silicon-oxy-nitride film, is therefore finer than a silicon oxide film, and, therefore, provides a superior barrier characteristic to moisture coming in from the outside. A semiconductor device having superior reliability such as moisture resistance can thus be provided.